Air source heat pumps are highly efficient renewable heating systems.
provides a renewable energy alternative for off-gas homes that could also earn you money through government payments. But what is an air source heat pump, how does it work and is it the right choice for your home?
What are air source heat pumps?
Air source heat pumps take heat from the air outside (even at low temperatures of -25 C). It then uses this heat to warm up your home.
They can either be fitted alongside a boiler (as a hybrid heating system) or on their own.
How do air source heat pumps work?
- The pump has a fan which brings in air from the outside and passes it over an exchanger coil.
- The exchanger coil contains a refrigerant liquid; the heat from the outside air causes the refrigerant to boil and evaporate, changing the refrigerant from liquid to vapour.
- This vapour passes through a compressor increasing the temperature of the vapour.
- This hot vapour heats a second exchanger coil which uses the energy generated to heat air or water for your home.
- The heat enters your home via an expansion valve. This valve also lowers the pressure and temperature so that the vapour turns back into a liquid and the process can repeat.
The performance of an air source heat pump is measured through a Coefficient of Performance (COP). This shows how many units of heat are produced per unit of energy it uses. On average, a heat pump has a COP of 3 as it produces 3 times as much energy as it uses. This gives heat pumps an efficiency of around 3,000%. To put that into context, modern boilers have efficiency levels of around 92%.
Types of air source heat pump
There are 2 types of air source heat pump to choose from: air-to-air or air-to-water.
Air-to-air pumps
Air-to-air pumps heat the home using fans. Like air conditioning in reverse. This type of pump doesn’t produce hot water.
Air-to-water pumps
An air-to-water pump heats water for radiators, underfloor heating systems and hot water for your taps.
Advantages or air source heat pumps
Heating and hot water for your home
Air source heat pumps can both heat your home and (if you choose air-to-water) your hot water. Some can even be used as air conditioners in the summer.
Earn money through RHI scheme
Air-to-water pumps are eligible for the government’s Renewable Heat Incentive (RHI) Scheme. This means you can earn money by heating your home with an air source heat pump.
High energy efficiency
Air source heat pumps produce 3-5 times energy as much as they use.
Cheaper heating bills
If you’re replacing an LPG, coal or electric heating system you should see a reduction in your heating bills.
Lower CO2 emissions
These pumps can significantly lower your home’s carbon footprint when replacing a conventional heating system.
Heating all year round
They can extract heat from the outside air even when temperatures are as low as -25° C (depending on the model).
Easy maintenance
A pump can last for as long as 20 to 25 years with the right maintenance and an annual service.
Disadvantages of air source heat pumps
Installation
An air source heat pump needs to be installed outside your home so you’ll need somewhere suitable. Air-to-water pumps can be difficult to retrofit.
To be carbon neutral, electricity must be green
Air source heat pumps are powered by electricity. So for a heat pump to be truly ‘green’, this electricity will need to be made by renewable energy sources.
Insulation
For this heating system to be as effective as possible your home needs to be well insulated. This is because air source heat pumps emit lower temperatures over a longer period.
Not always more efficient
If you’re replacing an old G rated boiler, coal, LPG or electric system then a heat pump is likely to be much cheaper to run. However, if you have an A rated gas or oil boiler, a heat pump may work out slightly more expensive.
Replacing radiators
Heat pumps are most effective if you have an underfloor heating system as they deliver lower temperatures more consistently. You may need to larger radiators to achieve the same level of heating in your home.
Water won’t be as hot
Compared to boilers, the hot water made by air source heat pumps isn’t as hot.
Inefficiency in cold weather
While air source heat pumps can still work at low temperatures, their energy efficiency decreases as the temperature drops as they have to work harder to extract heat.
Costs & savings
The average cost of installing an air source heat pump system falls between £5,000 – £11,000. This upfront cost can be recovered over time through both reduced energy bills and the government’s Renewable Heat Incentive (RHI) scheme. Potential savings will depend on the type of heating system you’re replacing, how you’ll use the energy generated and whether or not you can benefit from RHI payments.
The below table illustrates the potential savings using figures by the Energy Saving Trust based on an average 4 bed detached home.
| Existing Heating System | Energy Bill Savings per year? | Carbon Savings per year? |
|---|---|---|
| Old G rated Gas Boiler | £400 – £465 | 3,300 – 3,900kg |
| New A rated Gas Boiler | Increase of £35 – £55 | 1,200 – 1,400kg |
| Old G rated Oil Boiler | £460 – £545 | 5,200 – 6,100kg |
| New A rated Oil Boiler | Increase of £45 – £55 | 2,300 – 2,700kg |
| Old Electric Storage Heaters | £800 – £900 | 4,600 – 5,700kg |
| New Electric Storage Heaters | £465 – £545 | 3,200 – 3,800kg |
| Coal | £425 – £525 | 6,900 – 8,300kg |
Air Source Heat Pump Grants & Incentives
In addition to the potential savings in fuel bills and carbon emissions, air-to-water heat pumps can actually earn you money. Under the Renewable Heat Incentive (RHI) scheme the government will pay you for every unit (kWh) of energy you generate. Payments are made quarterly over 7 years.
We took a look at the potential RHI payments* to give you an idea of what you could earn.
| Detached Home (3 beds) | Payment per Quarter | Annual Payment | Total Earned Over 7 years |
|---|---|---|---|
| Replacing Gas or Oil System installed pre 2005 | £213 | £850 | £5,950 |
| Replacing Coal Fired System | £220 | £880 | £6,160 |
| Replacing Other Electricity System | £183 | £730 | £5,110 |
| Mid-Terrace Home (3 beds) | Payment per quarter | Annual payment | Over 7 years |
|---|---|---|---|
| Replacing Gas or Oil System installed pre 2005 | £180 | £720 | £5,040 |
| Replacing Coal Fired System | £188 | £750 | £5,250 |
| Replacing Other Electricity System | £155 | £620 | £4,340 |
| Mid-Terrace Home (3 beds) | Payment per quarter | Annual payment | Over 7 years |
|---|---|---|---|
| Replacing Gas or Oil System installed pre 2005 | £180 | £720 | £5,040 |
| Replacing Coal Fired System | £188 | £750 | £5,250 |
| Replacing Other Electricity System | £155 | £620 | £4,340 |
| Bungalow (2 or fewer bedrooms) | Payment per quarter | Annual payment | Over 7 years |
|---|---|---|---|
| Replacing Gas or Oil System installed pre 2005 | £173 | £690 | £4,830 |
| Replacing Coal Fired System | £170 | £680 | £4,760 |
| Replacing Other Electricity System | £145 | £580 | £4,060 |
*Calculated using the government’s BEIS Domestic Calculator using a tariff of 10.49p / kWh (valid for applications received before 01 July 2018). Based on a home located in England or Wales, built between 1976 – 1982, unknown amount of loft insulation and cavity walls with insulation. The calculations are intended as a representation only.
The best air source heat pumps
The best air source heat pumps are made by Daikin, Grant, Hitachi, LG, Mitsubishi, Samsung, Vaillant and Viessmann.
| Manufacturer | Popular Model | Available Outputs (kW) | ErP Rating | Potential Cost |
|---|---|---|---|---|
| Daikin | Altherma 3 | 4, 6, 8 | A++ | £6,000 – £8,000 |
| Grant | Aerona3 | 6-16 | A++ | £4,000 – £7,000 |
| Hitachi | YUTAKI S802 | 11, 14, 16 | A+++ | £4,000 – £6,000 |
| LG | Therma V R32 | 5-16 | A++ | £4,000 – £6,000 |
| Mitsubishi | Ecodan QUHZ | 4.5 | A++ | £4,000 – £6,000 |
| Nibe | F2040 | 8, 12, 16 | A+++ | £6,000 – £8,500 |
| Samsung | EHS Mono | 16 | A+++ | £3,750 |
| Vaillant | aroTHERM | 5, 8, 11, 15 | A+++ | £3,000 – £7,500 |
| Viessmann | Vitocal 200-A | 2.6 – 11 | A+++ | £5,500 – £9,000 |
Heat pump quotes and installation
If you have an A rated gas or oil boiler, air source heat pumps are generally not recommended as a replacement system. They are best suited to off-gas, well-insulated properties and new-build projects. In England and Scotland, as long as the installation meets certain criteria, you don’t need planning permission for an air source heat pump as it’s a permitted development. In Wales and Northern Ireland planning permission is required.
If you think an air source heat pump could be the right choice for your home, your next step is to get quotes for installation.
